[PATCH 1/7] xfs: take the ILOCK when accessing the inode core

Darrick J. Wong
2021-12-16T01:09:26Z

From: Darrick J. Wong <djwong@kernel.org>

I was poking around in the directory code while diagnosing online fsck
bugs, and noticed that xfs_readdir doesn't actually take the directory
ILOCK when it calls xfs_dir2_isblock. xfs_dir_open most probably loaded
the data fork mappings and the VFS took i_rwsem (aka IOLOCK_SHARED) so
we're protected against writer threads, but we really need to follow the
locking model like we do in other places. The same applies to the
shortform getdents function.

While we're at it, clean up the somewhat strange structure of this
function.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
---
fs/xfs/xfs_dir2_readdir.c | 28 +++++++++++++++++-----------
1 file changed, 17 insertions(+), 11 deletions(-)

diff --git a/fs/xfs/xfs_dir2_readdir.c b/fs/xfs/xfs_dir2_readdir.c
index 8310005af00f..25560151c273 100644
--- a/fs/xfs/xfs_dir2_readdir.c
+++ b/fs/xfs/xfs_dir2_readdir.c
@@ -507,8 +507,9 @@ xfs_readdir(
size_t bufsize)
{
struct xfs_da_args args = { NULL };
- int rval;
- int v;
+ unsigned int lock_mode;
+ int error;
+ int isblock;

trace_xfs_readdir(dp);

@@ -522,14 +523,19 @@ xfs_readdir(
args.geo = dp->i_mount->m_dir_geo;
args.trans = tp;

- if (dp->i_df.if_format == XFS_DINODE_FMT_LOCAL)
- rval = xfs_dir2_sf_getdents(&args, ctx);
- else if ((rval = xfs_dir2_isblock(&args, &v)))
- ;
- else if (v)
- rval = xfs_dir2_block_getdents(&args, ctx);
- else
- rval = xfs_dir2_leaf_getdents(&args, ctx, bufsize);
+ lock_mode = xfs_ilock_data_map_shared(dp);
+ if (dp->i_df.if_format == XFS_DINODE_FMT_LOCAL) {
+ xfs_iunlock(dp, lock_mode);
+ return xfs_dir2_sf_getdents(&args, ctx);
+ }

- return rval;
+ error = xfs_dir2_isblock(&args, &isblock);
+ xfs_iunlock(dp, lock_mode);
+ if (error)
+ return error;
+
+ if (isblock)
+ return xfs_dir2_block_getdents(&args, ctx);
+
+ return xfs_dir2_leaf_getdents(&args, ctx, bufsize);
}